The invention relates to a machine for cutting rolls or logs, formed by wound web material, to form a plurality of shorter rolls. The invention relates also to a method for cutting logs and forming small rolls therefrom.
More particularly, the invention relates to a cutting machine comprising a unit rotating about an axis parallel to the axis of the log to be cut and carrying a cutting tool rotating about an axis parallel to the axis of rotation of said unit.
Presently known cutting machines of this type are able to carry out cutting operations with the log at a standstill. Once the log to be cut has been placed on the machine guide and fastened thereon, the rotating blade of the machine cuts a small roll while the log remains stationary. When the blade is clear of the log, the latter is moved forward an increment equal to the length of the roll to be cut, and then stopped again to perform the next cut. These machines work, therefore, in an intermittent manner. This creates lost work times and drawbacks due to the intermittent motion imparted to the log and, in particular problems of inertia due to difficulties in controlling the log motion, frequently leading to non-uniform lengths of the small rolls.
In view of the above, cutting machines have been studied in which the cutting of the log takes place by keeping the log in motion also during the cutting operation. Such a machine is described in U.S. Pat. No. 4,041,813. In these machines, the rotary cutting blade is carried by a unit which, in turn, rotates about an axis inclined to the axis of the log to be cut. In this way, as the blade-carrying unit rotates, the blade moves with a motion which has, on a horizontal plane, which passes through the axis of the log to be cut, a component which is parallel to the log axis. Since whatever the angular position of the blade-carrying unit, the blade of the cutting tool has to lie always in a plane perpendicular to the axis of the log to be cut, and thus these machines require a complex kinematic system which keeps the axis of the cutting blade constantly parallel to the log axis. An oscillatory motion of the tool axis with respect to the tool-carrying unit is thus obtained.
These second types of machines have a particularly complex construction. Moreover, the law of motion of the cutting tool is not the optimal one, because the tool motion, as projected onto the horizontal lying plane of the axis of the log to be cut, is a sinusoidal motion.
It is, therefore, an object of the invention to provide a cutting machine as above defined which allows, by a particularly simple and reliable structure, the cutting of logs which are continuously moving.
These and other objects, which will appear evident to those skilled in the art by the following description, are achieved by a machine characterized by means which give said cutting tool a reciprocating forward and backwards motion parallel to the axis of the log to be cut, said tool having a translation speed during the cutting step which is substantially equal to the feeding speed of the log to be cut.
Among the several advantages obtained in this way, the first to be mentioned is the increase of productivity and, secondly, a greater uniformity of the finished product. In fact, since the log to be cut is never brought to a definite stop, the phenomena of inertia, which in the known machines cause the cutting of small rolls of different lengths, are much reduced or even eliminated.
In one embodiment of the machine according to the invention, the means for imparting the reciprocating motion to the cutting tool are combined to the bearing shaft of the rotating unit on which said cutting tool is supported. A particularly compact structure is thus obtained. In practice, a cam may be secured to said shaft to cooperate with a fixed tappet.
To achieve the above-mentioned advantages of higher productivity and elimination of inertia phenomena, it is not necessary that the feeding speed of the log to be cut be constant. On the contrary, provision may be made for the speed to vary between a minimum value during the cutting, that is, when the tool is within the log to be cut, and a maximum value, when the tool is cleared of the log. This brings about the advantage of limiting the forward travel of the tool and thus the resulting accelerations, with a substantial reduction of mass and size of the cutting means, without the logs being stopped and, therefore, with consequent less inconveniences due to the inertia of the logs.
This makes it possible also to build a machine in which the length of the small rolls can be easily changed, as it will be apparent from the following description of an exemplary embodiment. In this case-, there must be provided means for feeding the log to be cut and means which connect said log-feeding means to the means which impart the rotational motion to said rotating unit. The connection means ensure the synchronism between the motion of the rotating unit and the motion of the feeding logs. The connection can be of the mechanical type, or an electronic connection may be provided through programming means such as a microprocessor, or other means capable of maintaining the synchronism between the motion of the logs feeding means and the driving means of the rotary unit. In this way, provision may be made for the connection means to impart a motion at variable speed to the log-feeding means while said rotary unit moves at constant speed.
The invention further relates to a method for transversely cutting logs to form small-size rolls, wherein the log is fed to a cutting group comprising a tool for transversely cutting the logs, said tool rotating about its own axis and about an axis which is parallel to the tool axis and parallel to the axis of the log to be cut, characterized in that the log is moved forward by a continuous motion, the cut taking place with the log in motion while the tool moves at a speed equal to that of the log.
In a particularly advantageous embodiment, the log is moved forward at a varying speed, that is at a reduced speed during the cutting operation and at a higher speed between subsequent cuttings. The higher speed may be adjusted to change the length of the small rolls obtained from the cutting of the logs.
Further advantageous embodiments of the present invention are set forth in the appended claims.
With the above and other objects in view, more information and a better understanding of the present invention may be achieved by reference to the following detailed description.